async_std/result/
from_stream.rs

1use std::pin::Pin;
2
3use crate::prelude::*;
4use crate::stream::{FromStream, IntoStream};
5
6impl<T, E, V> FromStream<Result<T, E>> for Result<V, E>
7where
8    T: Send,
9    E: Send,
10    V: FromStream<T>,
11{
12    /// Takes each element in the stream: if it is an `Err`, no further
13    /// elements are taken, and the `Err` is returned. Should no `Err`
14    /// occur, a container with the values of each `Result` is returned.
15    ///
16    /// # Examples
17    ///
18    /// ```
19    /// # fn main() { async_std::task::block_on(async {
20    /// #
21    /// use async_std::prelude::*;
22    /// use async_std::stream;
23    ///
24    /// let v = stream::from_iter(vec![1, 2]);
25    /// let res: Result<Vec<u32>, &'static str> = v.map(|x: u32|
26    ///     x.checked_add(1).ok_or("Overflow!")
27    /// ).collect().await;
28    /// assert_eq!(res, Ok(vec![2, 3]));
29    /// #
30    /// # }) }
31    /// ```
32    #[inline]
33    fn from_stream<'a, S: IntoStream<Item = Result<T, E>> + 'a>(
34        stream: S,
35    ) -> Pin<Box<dyn Future<Output = Self> + 'a + Send>> 
36    where
37        <S as IntoStream>::IntoStream: Send,
38    {
39        let stream = stream.into_stream();
40
41        Box::pin(async move {
42            // Using `take_while` here because it is able to stop the stream early
43            // if a failure occurs
44            let mut is_error = false;
45            let mut found_error = None;
46            let out: V = stream
47                .take_while(|elem| {
48                    // Stop processing the stream on `Err`
49                    !is_error
50                        && (elem.is_ok() || {
51                            is_error = true;
52                            // Capture first `Err`
53                            true
54                        })
55                })
56                .filter_map(|elem| match elem {
57                    Ok(value) => Some(value),
58                    Err(err) => {
59                        found_error = Some(err);
60                        None
61                    }
62                })
63                .collect()
64                .await;
65
66            if is_error {
67                Err(found_error.unwrap())
68            } else {
69                Ok(out)
70            }
71        })
72    }
73}
async_std/result/from_stream.rs

async_std/result/
from_stream.rs
